In the prior art, in an image reading apparatus which is used in a copier, a scanner, a multi-function apparatus having the functions of the former is known to have an automatic document feeder called the ADF (Auto Document Feeder) for transferring the documents from an input tray through a transfer path to an output tray. There is also known an automatic document feeder for reading a document having its two first and second sides printed. In this device, the document is reversed at its leading end and trailing end by reversible rollers while it is being transferred. (for example, see JP-A-8-85649).
FIG. 17 shows a transfer route of the automatic document feeder of the prior art. As shown in FIG. 17, a document P placed on an input tray 100 with the first side (first page) thereof facing upward is fed to a feed path 102 by a feed roller 101. In the feed path 102, the document P is fed to feed rollers 103 which are suitably disposed according to cases. When the document P passes through a scanning position X, the first side of the document P is scanned by an image reading element such as a CCD or a CIS. When a sensor detects the trailing end of the document P after the first side thereof is scanned, reversible rollers 104 are stopped while nipping the trailing end of the document.
As shown in FIG. 18, bidirectional feed path the reversible rollers 104 reverse the transfer direction of the nipped document P to a return path 105. The document P is fed from the bidirectional feed path 105 again to a side upstream of the scanning position X. The leading and trailing ends of the document P are reversed. The document P is fed by the feed rollers 103, and when the document P passes through the scanning position X, the second side of the document P is scanned by the image read unit. When a sensor detects the trailing end of the document P after the second side of the document P is scanned, the reversible rollers 104 are again stopped in a state where the trailing end of the document P is nipped. Afterwards, the document P is sent back along the return path 105. When the document P is moved from the return path 105 again into the feed path 102, the document P is held in a state where the leading and trailing ends of the document P are reversed once more, that is, the first side of the document P is opposed to the scanning position X. The document P is delivered along the feed path 102 and is discharged into an output tray 106 with the first side thereof facing downward. As a result, both the first and second sides of the document P are scanned and the document P is discharged to the output tray 106 in the order that the sheets of the document P were placed on the input tray 100.